The 'border' property is a shorthand property for setting the same width, color and style on all four borders of an element. For example, the first rule below is equivalent to the set of four rules shown after it:

In the above example, the color of the left border will be black, while the other borders are red. This is due to 'border-left' setting the width, style and color. Since the color value is not specified on the 'border-left' property, it will be taken from the 'color' property. The fact that the 'color' property is set after the 'border-left' property is not relevant.

Note that while the 'border-width' property accepts up to four length values, this property only accepts one.

The outer part or edge of anything, as of a garment, a garden, etc.; margin; verge; brink.

Upon the borders of these solitudes.
Bentham.

In the borders of death.
Barrow.

2.

A boundary; a frontier of a state or of the settled part of a country; a frontier district.

3.

A strip or stripe arranged along or near the edge of something, as an ornament or finish.

4.

A narrow flower bed.

Border land, land on the frontiers of two adjoining countries; debatable land; -- often used figuratively; as, the border land of science. -- The Border, The Borders, specifically, the frontier districts of Scotland and England which lie adjacent. -- Over the border, across the boundary line or frontier.